The present invention relates to a method for manufacturing a tire tread strip for a pneumatic vehicle tire with additional shoulder cover strips of rubber material in the shoulder area.
Such methods are, for example, known from European Patent Application 0 131 122 and from German Patent 33 25 017. In both known methods a shoulder cover strip is embodied as a connecting strip between the sidewall and the tread strip. This cover strip is supposed to improve the bonding of the sidewall to the tread strip which are made of different rubber materials. The shoulder cover strip are extruded together with a tread strip on a multiple die extruder and are then connected to the tread strip. Since for improving the bonding of the sidewall to the tread strip material the shoulder cover strips require a relatively large contacting surface for producing a sufficient adhesive contact between the shoulder cover strip and the sidewall as well as between the shoulder cover strip and the tread strip, such shoulder cover strips are of a relatively large thickness and the shoulder cover strips and their bonding to the tread strip can be produced relatively reliably by joint extrusion.
Such thick shoulder cover strips, however, affect the driving properties of the tire. This must be taken into consideration for the construction and manufacture of the tire and must be continuously monitored.
The joint extrusion method for tread strips and shoulder cover strips provides for a good mixing of the shoulder cover strip material and also a heating within similar temperature ranges as for the commonly extruded tread strip. Due to the temperatures of the shoulder cover strip and the tread strip being matched to one another the well mixed material can be applied directly at the extruder in an automated fashion onto the tread strip.
For applications in which such thick shoulder cover strips are not required, it is desirable to use shoulder cover strips of a much reduced thickness in order to minimize the effect onto the performance of the tire, for example, rolling resistance and handling. Uniformly thin shoulder cover strips cannot be produced or produced only with considerable expenditures by the methods known from European Patent Application 0 131 122 or German Patent 33 25 017.
Die heads of an extruder for producing thin extrudates (die strips) are subject to increased soiling which may lead to increased production down time due to the increased cleaning requirements. The reliability of the quality of the thinly extruded strips is constantly at risk due to undiscovered remains within the thin gap of the die head. These remains can result in being intermixed during subseuently performed production processes and can also result in clogging of the die head so that only a partial formation of the shoulder cover strip will result.
Such thin shoulder strips are, for example, suitable for use in connection with tire tread strips of rubber mixtures containing silica in which for lowering the conductance resistance of the tread strip shoulder cover strips are used within the shoulder area which contain mainly carbon black as a filler. Despite the reduced electrical conductance of the silica tread strip, the shoulder cover strip that reduces the conductance resistance ensures conductance of electrostatic charge. For this purpose a very thin shoulder cover strip is sufficient. The thickness of the shoulder cover strip is only of minimal importance in regard to conductance. In order to not affect the performance and trueness properties of the tire, the shoulder cover strip must be embodied as thin as possible. Such a vehicle tire with silica contained in the tread strip and attached shoulder cover strips is, for example, known from European Patent Application 0 658 452.
It is also known to apply premanufactured cut-to-length shoulder cover strips by hand. A uniform thickness can, however, not be produced by manual application. An adaptation of the temperature and tackiness of the shoulder cover strip to the tread strip is possible only to a limited extent.
It is therefore an object of the present invention to provide a method for manufacturing a tread strip of a pneumatic vehicle tire with shoulder cover strips with which method even thin shoulder cover strips can be applied reliably with substantially uniform thickness in an automated process.